Interesting. By the way...I never get any sign in my Xorg.0.log as to the actual refresh rate that X is using, and for the life of me I can't find any utility that reports that. Any idea how I could get that?

...you had indicated that the real refresh rate was 59.9. If that were the case, this might make even more sense. The actual technical video aspects of this are way way out of my league, but here's something that makes sense to me:

60.05 - 59.9 = .06 = the difference in cycles/second.

Converting Hz to period...that is the number of seconds for one cycle...is the inverse: 1/Hz. For example, 60Hz = 1/60 or .016666 seconds per cycle. I believe that, if you do that with the above difference:

1/.06 = 16.66667

That "period", I believe, would be the amount of time it would take for that difference to wrap around and effectively line up again....even closer to what we're seeing...something like the very slow beat frequency you hear when two musical notes are just slightly different.